Method for fabricating gaN-based nitride layer

ABSTRACT

The present invention relates to a method for fabricating a gallium nitride(GaN) based nitride layer including a step of forming a wetting layer having of forming a wetting layer having a composition of In(x1)Ga(y1)N (0&lt;x1≦1, 0≦y1&lt;1, x1+y1=1) on the silicon carbide buffer layer, and a step of forming a nitride layer containing gallium and nitrogen on the wetting layer, thereby can implement an opto-electronic device of high efficiency and high reliability.

TECHNICAL FIELD

The present invention relates to a method for fabricating a galliumnitride (GaN) based nitride layer. More particularly, the presentinvention relates to a method for fabricating a GaN-based nitride layerof a high quality using silicon carbide (SiC) buffer layer and a wettinglayer.

BACKGROUND ART

In a process of manufacturing semiconductor devices, in order to grow agallium nitride (GaN) based nitride layer, i.e., a GaN-based nitridelayer, substrates composed of, usually, sapphire (Al₂O₃), siliconcarbide (SiC), or the like have mainly been used. They are differentfrom the GaN-based nitride layer in terms of their physical propertiessuch as lattice constant and coefficient of thermal expansion. Thus, itis difficult to grow the GaN-based nitride layer of a high quality.Therefore, lots of schemes for growing the GaN-based nitride layer havebeen presented continually.

The most representative one includes a method of using a buffer layer.In this method, an Al(x)Ga(y)In(z)N(0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) layeris grown alone or through several combinations at a temperature rangingfrom 450° C. to 600° C. The growth of the Al(x)Ga(y)In(z)N layer isstopped and the temperature is then increased. Then, Al(x)Ga(y)In(z)N(0≦x≦1,0≦y≦1,0≦z≦1, x+y+z=1) that has been grown at a low temperaturebecomes nuclei. A GaN-based nitride layer of a high quality is grownusing the nuclei as a seed. This buffer layer includes an AlN bufferlayer (U.S. Pat. No. 4,855,249), an AlGaN buffer layer (U.S. Pat. No.5,290,393), an AlInN buffer layer (U.S. Pat. No. 6,508,878) and thelike.

However, although the GaN-based nitride layer is grown by this method,there is a problem in that the GaN-based nitride layer has a dislocationdensity of about 10¹⁰ to 10¹²/cm².

As an alternative, a buffer layer is not grown on a sapphire substrateat a low temperature as above, but a GaN-based nitride layersemiconductor is grown immediately on a substrate at a high temperature.However, this method has lots of room for improvement.

Meanwhile, researches on a method for growing silicon carbide (SiC) on asapphire wafer have rarely been made. However, M. C. Luo demonstrated onhis report that silicon carbide grown on (0001) sapphire has a 6Hstructure by means of Raman scattering measurement and X-Ray.Diffraction (XRD) analysis method. However, this experiment is directedto analysis into the structure of a formed silicon carbide layer, butnot to a method for fabricating a GaN-based nitride layer having goodphysical properties on the silicon carbide layer.

Moreover, U.S. Pat. No. 6,242,764 discloses a method in which an AlGaNlayer of a high quality is grown on a sapphire or silicon carbidesubstrate using a single crystalline silicon carbide layer at a hightemperature (>1300° C.) as a buffer layer. As in the U.S. Pat. No.6,242,764, however, if the single crystalline silicon carbide layer isgrown on sapphire, mismatch rate becomes great between the twomaterials. Therefore, this method has disadvantages that a siliconcarbide layer having a pretty high thickness (approximately 5 μm) isneeded in order to grow the AlGaN layer of a high quality, and thethickly formed silicon carbide layer has a low adhesive strength withsapphire.

[Disclosure]

[Technical Problem]

Accordingly, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide amethod for growing a GaN-based nitride layer of a high quality on anon-single crystalline SiC buffer layer.

Another object of the present invention is to provide a method forgrowing a GaN-based nitride layer of a high quality by adding a wettinglayer on a SiC buffer layer to enhance adhesion with the SiC bufferlayer and the GaN-based nitride layer, and by optimizing the formationof the SiC buffer layer and the wetting layer.

[Technical Solution]

To achieve the above objects, according to the present invention, thereis provided a method for fabricating a GaN-based nitride layer,including a first step of forming a non-single crystalline siliconcarbide buffer layer having a thickness of 5 Å to 200 Å on a sapphiresubstrate, a second step of forming a wetting layer having a compositionof In(x1)Ga(y1)N (0≦x≦1, 0≦y1<1, x1+y1=1) on the silicon carbide bufferlayer, and a third step of forming a nitride layer comprising galliumand nitrogen on the wetting layer.

In order to form a silicon carbide layer used as a buffer layer, siliconand carbon are brought into reaction within a deposition apparatus. Thesilicon material or source may be SiH₄, Si₂H₆ or the like. The carbonmaterial or source may include CBr₄, CH₄, etc. More specifically, CBr₄or C_(x)H_(y) (where x are y are integers), or a combination thereof maybe used as a carbon precursor for growing the silicon carbide layer.

At this time, it is preferred that a growth temperature (T) of thesilicon carbide layer is within a range of 600° C.≦T≦990° C. If thetemperature is too low, the silicon carbide layer itself cannot beformed.

It is preferred that the thickness of the silicon carbide buffer layeris 5 Å to 200 Å. If the thickness exceeds 200 Å, it may be difficult tocontrol the shape of the GaN-based nitride layer that is grown on thesilicon carbide buffer layer. Also, the adhesive strength with thesapphire substrate and the silicon carbide layer can be weakened.

In order to grow the GaN-based nitride layer, a variety of materialssuch as TMIn, TMGa, TMAl, NH₃ and hydrazine may be used. Although thematerials of the thin layers as constituent elements of the presentinvention have been described particularly, it is to be noted that theyare merely illustrative and the present invention is not restricted tothose illustrated materials.

The wetting layer can be formed in a single layer having the samestoichiometric composition or in a combination of two or more layershaving different stoichiometric composition.

It is preferable that the wetting layer is grown at a temperature of400° C. to 900° C. A total thickness of the wetting layer is preferably100 Å to 500 Å. If the growth temperature of the wetting layer is toohigh, it can be difficult to control the shape of the GaN-based nitridelayer that is grown on the wetting layer.

It is preferred that the GaN-based nitride layer is grown at atemperature of 800° C. to 1200° C.

According to the present invention, there is provided a method forfabricating a GaN-based nitride layer in which the GaN-based nitridelayer is grown above a substrate, including the step of forming anon-single crystalline silicon carbide buffer layer on the substrateprior to growing the GaN-based nitride layer.

According to the present invention, there is provided a method forfabricating a GaN-based nitride layer, including a first step of forminga silicon carbide buffer layer on a substrate, a second step of forminga wetting layer having a composition of In(x1)Ga(y1)N (0<x1≦1, 0≦y1<1,x1+y1=1) on the silicon carbide buffer layer, and a third step offorming a nitride layer including gallium and nitrogen on the wettinglayer.

According to the present invention, there is provided a method forfabricating a GaN-based nitride layer in which the GaN-based nitridelayer is grown above a substrate, including the step of forming asilicon carbide buffer layer on the substrate at a temperature of 600°C. to 990° C. prior to growing the GaN-based nitride layer.

According to the present invention, there is provided a method forfabricating a GaN-based nitride layer in which the GaN-based nitridelayer is grown above a substrate, including the step of forming asilicon carbide buffer layer of 5 Å to 200 Å in thickness on thesubstrate prior to growing the GaN-based nitride layer.

[Advantageous Effects]

According to the present invention, a non-single crystalline SiC thinlayer that has a material different from existing Al(x)Ga(y)In(z)N(0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) grown by means of a MOCVD method and isgrown at a low temperature, is formed on a sapphire substrate as abuffer layer, or a wetting layer and a GaN layer is formed on the bufferlayer. Therefore, a GaN layer having good physical properties can beformed. It is thus possible to implement an opto-electronic device ofhigh efficiency and high reliability.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a second embodiment of the present invention;

FIG. 2 is a view showing the surface of a GaN layer 13 immediately afterit has been grown by the method described with reference to FIG. 1;

FIG. 3 is a view showing a method for forming a GaN layer according to afirst comparative example;

FIG. 4 is a view showing the shape of the surface of the GaN layerformed according to the first comparative example;

FIG. 5 is a view showing the shape of the surface of the GaN layerformed by the method according to a first embodiment of the presentinvention;

FIG. 6 is a view showing a method for forming a GaN layer according to asecond comparative example; and

FIG. 7 is a view showing the shape of the surface of a GaN layer formedby a method of the second comparative example.

MODE FOR INVENTION

The present invention will now be described in detail in connection withpreferred embodiments with reference to the accompanying drawings.

Generally, in order to grow a GaN-based nitride layer, substratescomposed of sapphire (Al₂O₃), silicon carbide (SiC), or the like havemainly been used. Among them, the sapphire substrate is most frequentlyused due to its low price and good mechanical characteristics. Since thesapphire substrate has physical properties (lattice constant,coefficient of thermal expansion, etc.) different from the GaN-basednitride layer, it is difficult to grow a nitride layer of a highquality. As a result, the GaN-based nitride layer has a dislocationdensity of about 10¹⁰ to 10¹²/Icu.

On the contrary, the lattice mismatch of lattice constant betweensilicon carbide (SiC) and gallium nitride (GaN) is 3.3%. This issignificantly lower than 13.8%, which is the lattice mismatch of latticeconstant between sapphire (Al₂O₃) and gallium nitride (GaN). Thus, ingrowing the GaN-based nitride layer on sapphire (Al₂O₃), silicon carbide(SiC) can be used as a good buffer layer, and the second embodiment ofthe present invention is based on such technological concept.

As in the second embodiment of the present invention, however, when aGaN layer is grown on a SiC buffer layer, various characteristics appeardepending on the growth conditions (SiC growth temperature, GaN layergrowth temperature, III/V ratio, etc.). In particular, if a GaN-basednitride layer, for example, a GaN layer is grown at a high temperature,the adhesive strength between SiC and GaN is not good. For this reason,it has been found that in an initial state, a continuous GaN layer isnot evenly formed on the entire substrate but a discontinuous GaN layerexists. To combine the discontinuous GaN layer with the SiC bufferlayer, the GaN layer must be grown to a significant thickness.

Therefore, in the first embodiment of the present invention, in order toenhance adhesion between the SiC buffer layer and the GaN-based nitridelayer that will be grown on the SiC buffer layer, a wetting layercomposed of In(x1)Ga(y1)N (0≦x1≦1, 0≦y1<1, x1+y1=1) is employed. Theappropriate growing condition was found by understanding that thecharacteristic of the GaN-based nitride layer formed on the wettinglayer is greatly influenced by the growth conditions of the wettinglayer.

In both comparative example and an embodiment below, a MOCVD method isemployed and a sapphire substrate is used. The GaN layer is grown underthe same condition in both cases.

FIRST COMPARATIVE EXAMPLE

FIG. 3 is a view showing a method for forming a GaN layer according tothe first comparative example.

Referring to FIG. 3, a SiC buffer layer 12 is formed on a sapphiresubstrate 11. At this time, SiH₄ and CBr₄ are used as a source and agrowth temperature of 900° C. is used. The growth temperature of the SiCbuffer layer 12 is significantly lower than that (>1300° C.) of commonsingle crystalline silicon carbide. While non-single crystalline siliconcarbide is formed, mismatch between the sapphire substrate 11 and awetting layer that will be described later on can be mitigatedsufficiently.

Thereafter, a wetting layer 20 composed of In_(0.02)Ga_(0.98)N is formedon the SiC buffer layer 12. At this time, TMIn, TMGa and NH₃ are used assources and a growth temperature of 800° C. is used. Also, in the stepof forming the wetting layer 20, the ratio of V-group element toIII-group element (V/III ratio) is set to be within a range between 5000and 6000.

Next, a GaN layer 13 is formed on the wetting layer 20. At this time,the growth condition of the GaN layer is the same as the typical one. Ata temperature of approximately 800 to 1200° C., the V/III ratio is setto be within a range between 500 and 20,000.

FIG. 4 shows the shape of the surface of the GaN layer that is formed bythe method described with reference to FIG. 3. From FIG. 4, it can beseen that a problem is caused because lots of hillocks exist on thesurface of the GaN layer 13 although a discontinuous GaN layer 13 is notformed. The reason these hillocks exist will be described as follows.

In order to obtain a GaN layer having a good surface like a mirror, itis required that a wetting layer be grown in a direction vertical to thegrowth direction of a thin layer at the early stage of growth. Thismeans that III-group element and V-group element must move in thedirection parallel to the growth surface and be then uniformly combinedon the entire growth surface. If the amount of the V-group elementbecomes too much, the III-group element does not have the time formoving uniformly onto the entire growth surface and is mainly grown inthe direction vertical to the substrate, thus causing hillocks to occur.Therefore, if the amount of the V-group element is reduced, theIII-group element can have the time for moving uniformly onto the entiregrowth surface. Therefore, a GaN layer having a good surface like amirror can be obtained. The mobility for moving in the lateral directionon the surface can vary depending on Ga, In, Al and a combinationthereof, i.e., according to the type of the III-group elements, so thatthe growth condition for securing a sufficient plane mobility speed isaffected by the components of the wetting layer. Accordingly, AlN canhave a flatter surface at a high temperature when it has a lower V/IIIratio.

First Embodiment

The structure of the first embodiment according to the present inventionis formed by almost the same method as that described in the firstcomparative example. That is, all process steps and conditions are thesame as those of the first comparative example except that in the stepof forming the wetting layer 20, the V/III ratio is set to a rangebetween 250 and 300, which is 1/20 lower than that of the firstcomparative example. As such, the structure according to the firstembodiment of the present invention is the same as that shown in FIG. 3.Thus, description on it will be omitted in order to avoid redundancy ofexplanation.

FIG. 5 is a view showing the shape of the surface of the GaN layerformed by the method of the first embodiment according to the presentinvention. From FIG. 5, it can be seen that hillocks that can be seen inFIG. 4 almost disappear and a good surface like a mirror is obtained.

Through the results of the first embodiment, it can be seen that theV/III ratio is set to a range from 1 to 5000 in the step of forming thewetting layer 20 and it is preferred that the V/III ratio is lower thanthe V/III ratio, which is causes hillocks to occur in the GaN layer 13.

SECOND COMPARATIVE EXAMPLE

The second comparative example is intended to determine the effect ofthe SiC buffer layer. The structure of the second comparative example isformed by almost the same method as the first embodiment. That is, allprocess steps and conditions are the same as those of the firstembodiment except that the SiC buffer layer is not formed. FIG. 6 showsthe structure of the second comparative example. FIG. 7 shows the shapeof the surface of the GaN layer formed by the method according to thesecond comparative example.

From FIG. 7, it can be seen that the flat surface shown in FIG. 5 ischanged to a surface that is filled with very dense hillocks asformation of the SiC buffer layer is omitted. This is because the SiCbuffer layer serves to mitigate mismatch among the sapphire substrateand the wetting layer, and the GaN layer formed thereon.

Second Embodiment

FIG. 1 is a view showing the second embodiment of the present invention.As shown in FIG. 1, after a SiC buffer layer 12 has been formed on asapphire substrate 11, a GaN layer 13 is grown immediately on the SiCbuffer layer 12 at a high temperature of 900° C. or more.

FIG. 2 is a view showing the surface of the GaN layer 13 immediatelyafter it has been grown by the method described with reference toFIG. 1. Since the adhesive strength between SiC and GaN is not good, acontinuous GaN layer is not formed, but only a discontinuous GaN layer13 is formed. Therefore, in this case, it is necessary to grow a GaNlayer 13 having a thickness enough to overcome such discontinuousness.

1. A method for fabricating a GaN-based nitride layer including: a firststep of forming a non-single crystalline silicon carbide buffer layerhaving a thickness of 5 Å to 200 Å on a sapphire substrate; a secondstep of forming a wetting layer having a composition of In(x1)Ga(y1)N(0≦x1≦1, 0≦y1<1, x1+y1=1) on the silicon carbide buffer layer; and athird step of forming a nitride layer comprising gallium and nitrogen onthe wetting layer.
 2. The method for fabricating a GaN-based nitridelayer of claim 1, wherein in the first step, at least one of CBr₄ orC_(x)H_(y) (where x are y are integers) is used as a carbon precursor.3. The method for fabricating a GaN-based nitride layer of claim 1,wherein the growth temperature (T) of the silicon carbide buffer layeris within a range of 600° C.≦T<990° C.
 4. The method for fabricating aGaN-based nitride layer of claim 1, wherein the wetting layer is formedin a single layer.
 5. The method for fabricating a GaN-based nitridelayer of claim 1, wherein the wetting layer is formed in a combinationof two or more layers.
 6. The method for fabricating a GaN-based nitridelayer of claim 1, wherein the growth temperature of the wetting layer iswithin a range of 400° C. to 900° C.
 7. The method for fabricating aGaN-based nitride layer of claim 1, wherein the wetting layer has athickness of 100 Å to 500 Å.
 8. The method for fabricating a GaN-basednitride layer of claim 1, wherein in the second step, the V/III ratiohas a value and the value is within a range of 1 to 5000 and is lowerthan a V/III ratio causing hillocks to occur in the nitride layer. 9.The method for fabricating a GaN-based nitride layer of claim 1, whereinthe nitride layer is made of a combination of two or more layers. 10.The method for fabricating a GaN-based nitride layer of claim 1, whereinthe growth temperature of the nitride layer is within a range of 800° C.to 1200° C.
 11. The method for fabricating a GaN-based nitride layer ofclaim 1, wherein in the third step, the V/III ratio has a value of 500to
 20000. 12. A method for fabricating a GaN-based nitride layer above asubstrate including: a step of forming a non-single crystalline siliconcarbide buffer layer on the substrate prior to growing the GaN-basednitride layer.
 13. The method for fabricating a GaN-based nitride layerof claim 12 further including: a step of forming a wetting layer havinga, composition of In(x1)Ga(y1)N (0≦x1≦1, 0≦y1<1, x1+y1=1) on the siliconcarbide buffer layer prior to growing the GaN-based nitride layer.
 14. Amethod for fabricating a GaN-based nitride layer including: a first stepof forming a silicon carbide buffer layer on a substrate; a second stepof forming a wetting layer having a composition of In(x1)Ga(y1)N(0<x1≦1, 0≦y1≦1, x1+y1=1) on the silicon carbide buffer layer at a firsttemperature; and a third step of forming a nitride layer containinggallium and nitrogen on the wetting layer at a temperature higher thanthe first temperature.
 15. A method for fabricating a GaN-based nitridelayer above a substrate including: a step of forming a silicon carbidebuffer layer on the substrate at a temperature of 600° C. to 990° C.prior to growing the GaN-based nitride layer.
 16. The method forfabricating a GaN-based nitride layer of claim 15 further including: astep of forming a wetting layer having a composition of In(x1)Ga(y1)N(0≦x1≦1, 0≦y1<1, x1+y1=1) on the silicon carbide buffer layer prior togrowing the GaN-based nitride layer.
 17. A method for fabricating aGaN-based nitride layer above a substrate including: a step of forming asilicon carbide buffer layer of 5 Å to 200 Å in thickness on thesubstrate prior to growing the GaN-based nitride layer.
 18. The methodfor fabricating a GaN-based nitride layer of claim 17 further including:a step of forming a wetting layer having a composition of In(x1)Ga(y1)N(0≦x1≦1, 0≦y1<1, x1+y1=1) on the silicon carbide buffer layer prior togrowing the GaN-based nitride layer.